1. Field of the Invention
The present invention relates to power regulators, and more particularly to a compensation offset adjustment scheme for fast reference voltage transitioning to improve the settle-down performance in response to transitions of the reference voltage.
2. Description of the Related Art
The output voltage of a power supply (e.g., voltage regulator) is adjusted to achieve better performance under certain operational conditions in some applications. For example, the desired voltage for a central processing unit (CPU) may be a first voltage V1 under normal operating conditions and a second, lower voltage V2 under a sleep-mode condition. The typical way to change the output voltage is to adjust the reference voltage of the voltage regulator. The transition from V1 to V2 may occur very quickly and the voltage regulator should be able to operate with stability under this transition period and settle down in a relatively short time after the voltage transition. A typical compensation network of the voltage regulator is optimized to achieve good transient response to changes at the output. The compensation parameters are not optimal, however, for dynamic reference voltage transitions. The system settle-down performance after any reference voltage changes depends on the lowest zero frequency of the compensation network, while the zero frequency position is defined based on the system transient and stability requirements. When the reference voltage transitions from one voltage to another, the error amplifier changes from one operational point to another point in order to move the output voltage to follow the new reference voltage. The compensation network settles down slowly to the new operational point, however, due to a low frequency zero. The slow settle-down event of the compensation network causes a relatively large difference between the reference voltage and the output voltage for a significant period of time.
It is desired to provide compensation offset adjustment that achieves fast reference voltage transitioning to improve settle-down performance in response to transitions of the reference voltage of a DC-DC voltage regulator.